Cutting tools need to have wear resistance, welding resistance, and fracture resistance. Therefore, cutting tools, in which a variety of coating layers are formed on surfaces of hard substrates such as WC-based cemented carbide or TiCN-based cermet, are widely used.
In general, although TiCN layers and TiAlN layers are widely used as such coating layers, various coating layers are under development for the purpose of improvement in wear resistance and enhanced fracture resistance.
For example, Patent Literature 1 discloses a coating in which Ti in a (TiAl)N-based coating layer is partially replaced with Si and describes that the oxidation of the coating can be suppressed. Patent Literature 2 discloses a (Ti, Al)N coating layer in which a flank face has a higher Ti proportion than a rake face. Furthermore, Patent Literature 3 discloses that a TiAlN-based hard coating with a thickness of 1 to 5 μm is formed on a surface of a substrate such that coarse grains, which are present in the hard coating and have a size not less than the thickness of the coating, are 5% by area or less and the surface roughness Ra thereof is 0.1 μm or less or the surface roughness Rz thereof is 1 μm or less, whereby the welding resistance and wear resistance of the hard coating are improved.
The following is a list of the aforementioned background art:
PTL 1: Japanese Unexamined Patent Application Publication No. 09-295204
PTL 2: Japanese Unexamined Patent Application Publication No. 2008-264975
PTL 3: Japanese Unexamined Patent Application Publication No. 2002-346812
However, as disclosed in Japanese Patent Application Publication No. 09-295204, wear resistance and fracture resistance are not necessarily sufficient even though a coating layer containing Ti, Al, and Si is formed, and therefore, further improvement in wear resistance and fracture resistance are desired. Furthermore, further improvement is requested even for a coating layer having a difference in Ti proportion between a rake face and a flank face as disclosed in Japanese Patent Application Publication No. 2008-264945 and for a coating layer in which a number of coarse grains in a surface of the coating layer is made small as disclosed in Japanese Patent Application Publication No. 2002-346812.
Accordingly, it is an object of the present invention to provide a cutting tool including a coating layer capable of increasing oxidation resistance and fracture resistance of a rake face and a flank face.